The present invention relates generally to spin-on glass materials and more specifically to light-absorbing spin-on glass materials for use as anti-reflective layers in photolithography and methods of producing the materials.
To meet the requirements for faster performance, the characteristic dimensions of features of integrated circuit devices have continued to be decreased. Manufacturing of devices with smaller feature sizes introduces new challenges in many of the processes conventionally used in semiconductor fabrication. One of the most important of these fabrication processes is photolithography.
It has long been recognized that linewidth variations in patterns produced by photolithography can result from optical interference from light reflecting off an underlying layer on a semiconductor wafer. Variations in photoresist thickness due to the topography of the underlying layer also induce linewidth variations. Anti-reflective coatings (ARC) applied under a photoresist layer have been used to prevent interference from reflection of the irradiating beam. In addition, anti-reflective coatings partially planarize the wafer topography, helping to improve linewidth variation over steps because the photoresist thickness is more uniform.
Organic polymer films, particularly those that absorb at the i-line (365 nm) and g-line (436 mn) wavelengths conventionally used to expose photoresists, and at the recently used 248 nm wavelength, have been employed as anti-reflective coatings. However, the fact that the organic ARC""s share many chemical properties with the organic photoresists can limit usable process sequences. Furthermore organic ARC""s may intermix with photoresist layers. One solution to avoid intermixing, is to introduce thermosetting binders as additional components of organic ARC""s, as described, for example in U.S. Pat. No. 5,693,691 to Flaim et al. Dyes may also be incorporated in organic ARC""s, as well as, optionally, additional additives such as wetting agents, adhesions promoters, preservatives, and plasticizers, as described in U.S. Pat. No. 4,910,122 to Arnold et al.
Silicon oxynitride is another material that has been used as an anti-reflective coating. However, silicon oxynitride works as an ARC by a destructive interference process rather than by absorption, which means that very tight control of the oxynitride thickness is necessary and that the material may not work well as an ARC over highly variable topography. Furthermore silicon oxynitride is typically deposited by chemical vapor deposition, while photoresist layers are typically applied using a spin-coater. The additional chemical vapor deposition process can add to processing complexity.
Yet another class of materials that can be used as an anti-reflective layer is spin-on-glass (SOG) compositions containing a dye. Yau et al., U.S. Pat. No. 4,587,138, disclose a dye such as basic yellow #11 mixed with a spin-on-glass in an amount approximately 1% by weight. Allman et al. U.S. Pat. No. 5,100,503 disclose a cross-linked polyorganosiloxane containing an inorganic dye such as TiO2, Cr2O7, MoO4, MnO4, or ScO4, and an adhesion promoter. Allman additionally teaches that the spin-on-glass compositions also serve as a planarizing layer. However, the spin-on-glass, dye combinations that have been disclosed to date are not optimal for exposure to the deep ultraviolet, particularly 248 and 193 nm, light sources that are coming into use to produce devices with small feature sizes. Furthermore, not all dyes can be readily incorporated into an arbitrary spin-on-glass composition.
What is needed is an absorbing spin-on-glass anti-reflective coating material that absorbs strongly and uniformly in the deep ultraviolet spectral region. It would be desirable for the ARC layer to be impervious to photoresist developers. It would also be desirable to provide a method to incorporate a range of absorbing compounds into a variety of SOG materials while retaining the desirable properties of the original spin-on-glass materials.
An anti-reflective coating material for deep ultraviolet photolithography includes one or more organic absorbing compounds incorporated into a spin-on-glass (SOG) material. The spin-on-glass materials include methylsiloxane, methylsilsesquioxane, phenylsiloxane, phenylsilsesquioxane, methylphenylsiloxane, methylphenylsilsesquioxane, and silicate polymers. As used herein, spin-on-glass materials also include hydrogensiloxane polymers of the general formula (H0-1.0SiO1.5-2.0)x and hydrogensilsesquioxane polymers, which have the formula (HSiO1.5)x, where x is greater than about 8. Also included are copolymers of hydrogensilsesquioxane and alkoxyhydridosiloxane or hydroxyhydridosiloxane. Spin-on-glass materials additionally include organohydridosiloxane polymers of the general formula (H0-1.0SiO1.5-2.0)n(R0-1.0SiO1.5-2.0)m, and organohydridosilsesquioxane polymers of the general formula (HSiO1.5)n(RSiO1.5)m, where m is greater than 0 and the sum of n and m is greater than about 8 and R is alkyl or aryl. Coating solutions of spin-on-glass materials incorporating absorbing comounds are used to form anti-reflecting films on various layers in integrated circuit devices.
Absorbing compounds suitable for use with the present invention are strongly absorbing at wavelengths less than about 375 nm or less than about 260 nm. In particular, suitable absorbing compounds are strongly absorbing over at least an approximately 10 nm wide wavelength range around wavelengths such as 248 nm, 193 nm, or other ultraviolet wavelengths, such as 365 nm, that may be used in photolithography. The chromophores of suitable compounds typically have from one to three benzene rings that may or may not be fused. Incorporatable absorbing comounds have an accessible reactive group attached to the chromophore, the reactive groups including hydroxyl groups, amine groups, carboxylic acid groups, and substituted silyl groups with silicon bonded to one, two, or three alkoxy group or halogen atom substituents. The reactive groups may be directly bonded to the chromophore or the reactive groups may be attached to the chromophore through a hydrocarbon bridge.
Examples of suitable organic absorbing compounds include anthraflavic acid, 9-anthracene carboxylic acid, 9-anthracene methanol, alizarin, quinizarin, primuline, 2-hydroxy-4(3-triethoxysilylpropoxy)-diphenylketone, rosolic acid, triethoxysilylpropyl-1,8-naphthalimide, 9-anthracene carboxy-methyl triethoxysilane, phenyltriethoxysilane, azo compounds, such as 4-phenylazophenol, and mixtures thereof.
According to another aspect of the present invention, methods for synthesizing absorbing spin-on-glass compositions are provided. Spin-on-glass materials are conventionally synthesized from silane reactants such as triethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, tetramethoxysilane, methytrimethoxysilane, trimethoxysilane, dimethyldimethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, diphenyldiethoxysilane, and diphenyldimethoxysilane. Halosilanes, particularly chlorosilanes, for example, trichlorosilane, methyltrichlorosilane, ethyltrichlorosilane, phenyltrichlorosilane, tetrachlorosilane, dichlorosilane, methyldichlorosilane, dimethyldichlorosilane, chlorotriethoxysilane, chlorotrimethoxysilane, chloromethyltriethoxysilane, chloroethyltriethoxysilane, chlorophenyltriethoxysilane, chloromethyltrimethoxysilane, chloroethyltrimethoxysilane, and chlorophenyltrimethoxysilane are also used as silane reactants.
A method of making an absorbing spin-on-glass composition includes combining one or more alkoxysilanes, or, one or more halosilanes, one or more incorporatable organic absorbing compounds, an acid/water mixture, such as a nitric acid/water mixture, and one or more solvents to form a reaction mixture; and refluxing the reaction mixture to form the absorbing spin-on-glass composition. The spin-on-glass composition so formed is diluted with one or more solvents to provide coating solutions that produce films of various thicknesses. Alternative methods of making an absorbing spin-on-glass composition, including methods using halosilanes and a phase transfer catalyst, are also provided.
According to yet another aspect of the invention, the absorbing compound of the chemical composition 9-anthracene carboxy-methyl triethoxysilane is provided. A method of synthesizing 9-anthracene carboxy-methyl triethoxysilane includes combining 9-anthracene carboxylic acid, chloromethyltriethoxysilane, triethylamine, and a solvent to form a reaction mixture; refluxing the reaction mixture; cooling the refluxed reaction mixture to form a precipitate and a remaining solution; and filtering the remaining solution to produce liquid 9-anthracene carboxy-methyl triethoxysilane.